N-Acetylcarnosine (NAC) is a naturally-occurring compound chemically related to the dipeptide carnosine. Its molecular structure is similar to carnosine with the exception that it carries an additional acetyl group. This makes NAC a more stable molecule which is not easily destroyed by carnosinase, an enzyme that breaks down carnosine to its constituent amino acids, beta-alanine and histidine.; NAC is a free-radical scavenger and is particularly active against lipid peroxidation in the different parts of the lens in the eye. It is the active ingredient of eye drops used in order to prevent or treat cataract. [HMDB]

This compound belongs to the class of organic compounds known as hybrid peptides. These are compounds containing at least two different types of amino acids (alpha, beta, gamma, delta) linked to each other through a peptide bond.